In order to improve the impregnation properties of fiber bundles with a resin when producing a fiber-reinforced resin composition, various studies have been made on an impregnation chamber for impregnating the fiber bundles with the resin. As a result of these studies, current production methods can prevent the resulting resin composition from suffering from problems such as poor outward appearance or a decrease in strength when the number of fiber bundles introduced into one impregnation chamber is small.
However, when increasing the size of the device and introducing a number of fiber bundles into one impregnation chamber in order to increase the amount of production, impregnation of the fiber bundles with a resin becomes insufficient even when using the same production method, whereby poor outward appearance caused by unspread glass fibers or the like often occurs in spite of taking various measures. Moreover, the resin may be colored or show deterioration in hue to cause a further deterioration in outward appearance. Therefore, a resin composition mass-produced using a large device is limited in application to products for which particularly good outward appearance is required, or must be colored using a large amount of pigment such as carbon black to cover unspread glass fibers, coloration of the resin, or a change in hue. In particular, black products such as automobile parts suffer from unspread glass fibers, lightly pigmented products such as household articles suffer from coloration (colored foreign matter) and unspread glass fibers, and unpigmented products such as household appliance parts suffer from a change in hue, coloration, and unspread glass fibers.
Patent document 1 discloses a method of impregnating three individual fiber bundles with a molten resin at the same time. However, since this method introduces the resin from one point on one side of a die (impregnation chamber), the flow rate and the resin pressure of the resin differ to a larger extent between the position close to the extruder and the position away from the extruder as the number of fiber bundles is increased. Moreover, since the flow of the resin in the direction perpendicular to the fiber bundle progress direction becomes predominant, outward appearance rapidly deteriorates due to unspread fibers, organic foreign matter, deterioration in hue, and the like. Therefore, application of this method to products for which good outward appearance is required is limited. Moreover, since the resin is not sufficiently supplied to the fiber bundles away from the extruder, the withdrawing rate cannot be increased. This results in poor productivity, there by making it impossible to deal with mass production.
Patent document 2 discloses a method in which a cylindrical die box (impregnation) is disposed in the vertical direction, and four fiber bundles are impregnated at the same time. However, this method has a problem in which the number of fiber bundles to be loaded is limited Moreover, since the volume of the die box must be increased as the number of fiber bundles is increased, only about four fiber bundles can be introduced. Moreover, since the fibers spread using a ring spreader are immediately bound in the ring spreader portion, unspread fibers tend to remain in the resulting molded article. Moreover, since the residence time of the resin is long and the resin tends to be retained in the fiber bundle withdrawing path, colored foreign matter is produced or deterioration in hue occurs. Since the direction of the fiber bundles is perpendicularly changed in the fiber bundle withdrawing path when withdrawing the fiber bundles, the withdrawing rate cannot be increased. Furthermore, since the cylindrical die box is disposed in the vertical direction, it is necessary to supply the resin at a high position. This makes it necessary to install the extruder at a high position, whereby the device installation place and the like are limited.    [Patent document 1] JP-A-10-264152    [Patent document 2] JP-A-7-62246
The invention has been achieved in view of the above-described situation. An object of the invention is to provide a method for producing a fiber-reinforced resin composition capable of mass-producing a fiber-reinforced resin composition (fiber-reinforced resin pellets) with excellent outward appearance.
In order to achieve the above object, the inventor has conducted extensive studies. As a result, the inventor has found the following problems resulting from known methods. Specifically, when increasing the size of the device in order to introduce a number of fiber bundles into one impregnation chambers the resin pressure in the impregnation chamber becomes non uniform due to the pressure loss in the impregnation chamber. When increasing the resin pressure in order to prevent insufficient supply of the resin, it becomes difficult to remove gas from the fiber bundles at a position at which the resin pressure is high such as in the vicinity of the resin flow inlet, whereby the impregnation properties deteriorate. Moreover, since the flow in the direction perpendicular to the fiber bundle progress direction is increased due to an increase in the size of the device, the flow of the resin in the impregnation chamber becomes nonuniform (i.e. unsymmetrical), whereby the resin tends to be retained at a specific area. This increases the average residence time of the resin in the impregnation chambers, whereby coloration of the resin or deterioration in hue is increased.
The inventor has examined the method of supplying the resin to the impregnation chamber and the method of loading the fiber bundles into the impregnation chamber (e.g. supply method loading method, and positions and numbers of resin flow inlets and inlets) based on the above findings. As a result, the inventor has found that it is effective to provide a plurality of resin flow inlets in the impregnation chamber near the fiber bundle inlet to regulate the flow of the resin and reduce the difference in resin pressure in the impregnation chamber. This finding has led to the completion of the invention.